Synthesis of functionalized liquid rubbers from polyisoprene

Noncatalytic transformation of cis ‐1,4‐polyisoprene rubber ( M n = 320,000) into functionalized liquid rubbers containing various amounts of carbonyl groups was studied. The process is performed via selective carboxidation of the polymer CC bonds by nitrous oxide (N 2 O) in the temperature range of 180–230°C and under 3–6 MPa pressure. The carboxidation proceeds by the nonradical type mechanism involving the 1,3‐dipolar cycloaddition of N 2 O to the CC bond. The main route of the reaction (ca. 65%) proceeds without cleavage of the internal CC bonds and leads to the formation of ketone groups in the polymer backbone. The second route (ca. 35%) includes the cleavage of CC bonds, yielding the molecules of a smaller size. This route results in a manifold decrease of the molecular weight, which, depending on the carboxidation degree, may be more than two orders of magnitude less than that of the parent rubber. A series of functionalized liquid rubbers having M n value from 1000 to 19,000, and the oxygen content from 0.3 to 3.9 wt % was obtained in the form of the liquid unsaturated polyketones. Similar polyketones can also be prepared by carboxidation of the natural rubber. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009